The cold has forced a kind of collective deconditioning for many runners this year, said Dr. Tamanna Singh, a cardiologist and director of the Sports Cardiology Center at the Cleveland Clinic. “Everybody’s kind of suffering together, as we get out of our winter slumber and try to build back our running base,” she said. (“I can usually handle a decent amount of winter,” she added. This year, she moved most of her workouts indoors.)